The present invention relates to an apparatus and a method for the alignment of disk-shaped substrates, especially semiconductor wafers, and includes an alignment detection unit.
In the semiconductor industry, to manufacture semiconductor elements generally semiconductor disks, also known as wafers, that are comprised of a single crystal, are subjected to various treatment processes. These treatment processes are greatly automated, and between the treatment processes the semiconductor disks are transported with handling devices, which are generally support plates. In this connection, a centered placement of the disks upon the support plates is important in order to ensure a proper positioning of the disks in the various treatment devices. In addition, the disks must be aligned in accordance with the axes of their crystal lattices. Both the centering as well as the alignment of the disks is undertaken by alignment apparatus, which are also designated as aligners.
With one known aligner, which is shown by way of example in FIGS. 11a–d, a semiconductor disk 1 is deposited by a handling device 2 upon support pins 3 of the aligner. The handling device is subsequently moved out of the region below the wafer and the pins 3 are lowered, as a result of which the disk is positioned upon the rotary turntable 4, which is designated as a chuck. The rotary turntable 4 is provided with an underpressure suction device in order to securely hold the disk thereon. If the disk 1 is attached by suction, the rotary table 4 is rotated about its axis of rotation. During this rotation, a lateral displacement of the disk relative to the axis of rotation is measured with a camera 5. The pins 3 are again raised in order to raise the semiconductor disk 1 from the rotary table 4, and the pins are moved in a horizontal direction as a function of the measured displacement in order to center the disk relative to the rotary table 4. Subsequently, the disk is again deposited upon the rotary turntable 4 in order to repeat the above measurement process and to ensure that the disk 1 is now centered relative to the rotary turntable 4. This process is repeated until a complete centering is achieved.
In addition to the measurement of the lateral displacement, the camera 5 is in a position to recognize a marking in the form of a recess, which is also known as a notch, or to recognize a flattened portion of the edge of the disk 1, which is also known as a flat, with the notch or flat providing the crystal direction of the disk. After the aforementioned centering, the rotary turntable 4 is rotated in a desired direction in order to bring the marking into a predetermined position. The positioning is monitored by the camera, which then also simultaneously reads the ID number that is formed in the semiconductor disk and that has, for example, the form of a barcode or a number sequence.
The alignment process described above is very complicated and expensive, and since it includes a plurality of steps that are to be repeated, it is also very time intensive, which results in a very low throughput. Furthermore, a comprehensive software is necessary for the control of the various elements, and also a suction device is necessary for holding the disks on the rotary turntable, which unnecessarily increases the cost for the apparatus.
Due to mechanical movements of motors or other components of the unit, resonance effects that produce vibrations can occur, due to which a disk that rests upon the pins can be shifted and can thus influence the centering. A further problem results due to the suction of the wafer against the rotary turntable, since as a consequence dust particles that are in the environment can be suctioned on and which collect on the surface of the wafer over a large surface area thereof in the region of the suction openings, as shown in FIGS. 12a and 12b. 
Contaminations of this type can, however, greatly adversely affect the usability of the semiconductor disk.
FIG. 12a shows the underside of a semiconductor disk 1 before it is suctioned onto a rotary turntable, and FIG. 12b shows the surface of the wafer after the suctioning onto the rotary turntable. As can be seen in FIG. 12a, a small amount of contamination is found on the underside of the wafer and is distributed over the entire surface. However, as can be recognized in FIG. 12b, due to the suctioning of the semiconductor disk a large number of particles collect on the underside, and in particular in the region in which the suction device of the rotary turntable suctions the disk 1.
DE-A-35 06 782 discloses an apparatus for the alignment of the edges of a wafer, according to which the wafer is again positioned on a rotary turntable. The rotary turntable has an underpressure suction device in order to securely hold the disk thereon. During the time that the disk is suctioned on, the rotary turntable is rotated about its axis of rotation, and a lateral displacement of the disk relative to the axis of rotation is measured with the aid of a series of photo detectors in order to be utilized for the subsequent centering of the wafer.
U.S. Pat. No. 3,982,627 describes an apparatus for the automatic alignment of a wafer, according to which the wafer is placed upon an inclined support. Due to the incline, the wafer slides against a rotatable abutment. For the alignment of the wafer, the rotatable abutment, and hence the wafer, are rotated until the wafer achieves a desired position. During the rotation of the wafer, it is held spaced from the support via an air cushion.
Proceeding from the previously described apparatus, it is an object of the present invention to provide an apparatus and a method for the alignment of disk-shaped substrates, in particular semiconductor wafers, which use an alignment detection unit and which, in a simple and economical manner, enable an alignment of the substrate and permit a simple integration into existing wafer treatment units. In this connection, an alignment involves not only a spatial arrangement but also a certain rotational arrangement of the substrate.